Friction materials as heretofore used to form braking members utilize asbestos in the form of being dispersed in and integrated by organic or inorganic binders. However, these show insufficient heat resistance and frictional wear properties, e.g., friction coefficient and wear resistance, that tend to drop in the high-temperature range, resulting in the increased occurrence of a fading phenomenon when braking is effected. When braking is effected, the contact of such friction materials with a high-speed brake disc causes the frequent occurrence of “braking noise”. Also, asbestos is a known cancer-causing substance and is readily made into dusts. In view of the environmental hygienic problem that workers may inhale asbestos during operation, the use of asbestos has been increasingly self-restrained. Under these circumstances, it has been strongly demanded to develop asbestos substitutes.
In response to such demands, friction materials using non-carcinogenic potassium titanate fibers as a friction control agent have been proposed and achieved a widespread use for incorporation primarily in automobile braking pads. The friction materials containing potassium titanate fibers exhibit superior sliding properties and good braking effect. Nevertheless, they provide little damage to braking discs, which is a very favored advantage thereof. However, they suffer from insufficient wear resistance, particularly in the high-temperature range, and a slightly faster wear rate. Also, they have not yet offered a sufficient solution to “braking noise” developed in braking devices. Further, the potassium titanate fibers, because of their fibrous form, are bulky and poor in flowability, leading to their tendency to deposit on a wall of a feed passage and block the passage during manufacture of friction materials, which has been a problem.
Japanese Patent Laying-Open No. Hei 5-221759 describes potassium magnesium titanate having an orthorhombic layer structure, i.e., lepidocrocite potassium magnesium titanate, with a composition represented by the formula K0.8Mg0.4Ti1.6O4, a major diameter (length) of 5 mm, a minor diameter (breadth) of 2-3 mm and a thickness of 0.1-0.5 mm. Also, Japanese Patent Registration No. 3027577 describes the utility of lepidocrocite potassium magnesium titanate as a friction control agent for friction materials. Such friction materials exhibit stable frictional wear properties in the low-to high-temperature ranges. However, since a contact temperature between the brake disc and brake pad is high and reaches 1,000° C. or over, their heat resistance sometimes becomes insufficient for the long-term continuous use, e.g., for over several tens hours, possibly resulting in the reduced wear resistance in the high-temperature range and the increased wear amount. There accordingly remains a need for development of friction materials with further improved heat resistance and frictional wear properties.